1. Field of the Invention
This invention relates to method and apparatus for monitoring the position of a sheet strip material passed through a stamping device, and more particularly, to a method and apparatus for detecting a sheet strip material misfeed condition within the stamping device as the sheet strip material progresses through the stamping device.
2. Description of the Prior Art
It is well known in the stamping art to pass a sheet strip material through a stamping device to produce a plurality of individual frames or stampings in the sheet strip material. The individual frames or stampings each have a configuration dependent upon the placement of the various punches in the movable portion of the stamping device. As the sheet strip material is passed through the stamping device, the movable portion of the stamping device is cycled into and out of contact with the sheet strip material to blank stock from the sheet strip material to provide a plurality of individual frames or stampings. After the individual frames exit the stamping device, the individual frames may be separated from one another for further use.
Since the stamping device operates at a high rate of speed, a sheet strip material misfeed condition within the stamping device resulting in frames being produced having an undesired configuration is normally undetected unless the stamping device operator shuts the system down and performs a visual inspection of the individual frames or stampings. Generally, by the time the operator stops the stamping device to inspect the individual frames or stampings, the misfeed condition results in a large number of frames or stampings being produced having an undesirable configuration. These frames or stampings must be removed from the sheet strip material for scrap.
As known in the art, a sheet strip material misfeed condition is identified as any condition, occurring either internally or externally to the stamping device, which prevents the sheet strip material from being at its proper location within the stamping device at any preselected instant of time relative to the movable portion of the stamping device.
In order to provide an early indication of a sheet strip material misfeed condition within the stamping device, various devices have been utilized.
Spring loaded micro-switches or other suitable contact-type switches have been employed internal to the stamping device to provide a material misfeed indication to the stamping device operator if the sheet strip material passing through the stamping device rolls over on itself or buckles within the stamping device. When this roll-over or buckle condition occurs, up to three layers of sheet strip material are provided to the movable punch assembly portion of the stamping device. When this occurs, the movable punch assembly is inhibited in its length of travel and, as a result, the micro-switch is not closed. If the micro-switch fails to close, a signal is provided to notify the stamping device operator of the roll-over or buckle condition. The use of a micro-switch or other mechanical contact-type switch internal to the stamping device is undesirable since these switches can only detect a roll-over or buckle condition when the movable portion of the stamping device is inhibited in its full length of travel. In addition, these switches will detect a roll-over or buckle condition only after the roll-over or buckling has occurred. The micro-switch cannot detect other types of misfeed conditions which may occur such as a change in the speed of the sheet strip material passing through the stamping device or a momentary jamming of the sheet strip material within the stamping device.
Therefore, there is a need for a non-contact detection apparatus for use with a stamping device that is capable of detecting a sheet strip material misfeed condition as the misfeed condition is occurring.
Although non-contact detecting devices are commercially available, these non-contact detecting devices are limited in that they only detect the thickness of a sheet strip material, or the presence or absence of a sheet strip material at a preselected location.
U.S. Pat. No. 2,587,631 discloses a method and device adapted to detect magnetic sheets which vary from a predetermined standard of thickness. U.S. Pat. No. 2,700,132 discloses a device for preventing the feeding of more than one thickness of magnetic sheet material into printing, fabricating or other sheet or blank treating machines, and includes an electronic double detector having an electromagnetic detecting head which is disposed in the path of travel of the sheets or blanks.
U.S. Pat. Nos. 2,994,015 and 3,069,601 disclose a magnetic detector for gauging or measuring the thickness of ferro-magnetic sheet material passed in proximity to a pair of magnetic detector heads.
U.S. Pat. No. 4,019,131 discloses a method and apparatus for measuring the shape of the wavy edges of metal strips. The measuring apparatus comprises an electromagnetic induction type non-contacting distance measuring device including a detection coil disposed near the edge of a running metal strip, a filter for deriving out the high frequency component and the low frequency component of the output of the detection coil, and means responsive to the high frequency component for determining the contour of the wavy edge of the strip. The device also includes a means responsive to the low frequency component for adjusting the lateral position of the detection coil with respect to the wavy edge of the metal strip.
U.S. Pat. No. 4,134,486 discloses a workpiece detection circuit in an article handling apparatus for aborting a workpiece from the apparatus whenever an unanticipated workpiece presence or absence is sensed.
U.S. Pat. No. 4,138,709 discloses a proximity switch which is adapted to close a circuit between a source and a load when a metal object is adjacent to the coil in the switch.
U.S. Pat. No. 4,420,747 discloses a sheet feed monitoring system for detecting missing or superimposed sheets fed to a sheet processing machine. The system includes a measuring device for generating signals increasing with the number of superimposed sheets and an evaluating device for emitting an electrical signal when irregularities occur.
While it has been suggested by the prior art devices to utilize contact-type switches to detect a sheet strip material roll-over or buckle condition within the stamping device and to utilize non-contact sensing devices to determine the thickness or presence of a sheet strip material at a preselected location, there is a need for an improved method and apparatus for detecting a sheet strip material misfeed condition within a stamping device as the misfeed condition is occurring. When the material misfeed condition is detected, the apparatus must be capable of providing a signal to the stamping device to initiate stoppage of the stamping device to allow the material misfeed condition to be corrected.